Rab proteins are small GTPases that regulate different exocytic and endocytic transport processes. Rab5 is involved in endocytosis and fusion between early endosomes and functions by recruiting its effector, rabaptin-5, from cytosol to early endosomes in a GTP-dependent manner. The function of rabaptin-5, however, is unknown.
The aim of this proposal is to study the role of rabaptin-5. Preliminary experiments indicate that rabaptin-5 belongs to a multiprotein complex. To identify the molecules interacting with rabaptin-5 and study their function, the complex will be isolated by chromatographic techniques and its constituents molecularly cloned. The assembly of the complex will be investigated biochemically and its functional role will be studied both in vitro in a cell-free early endosome fusion assay as well as in vivo in transfected cells. The two-hybrid system will also be used as an alternative approach to identify rabaptin-5 interacting partners. Our findings will help elucidating the molecular principles underlying the docking and fusion process in membrane transport.